But Mr Salmond has strongly disputed the figures, accusing UK ministers of peddling misinformation on the issue.

In its analysis on the set up costs, the Treasury said the figure could even be nearly twice as much as its own £1.5bn estimate, if based on a different study by Prof Patrick Dunleavy, of the London School of Economics.

"The first minister would be on much stronger territory challenging the Treasury's figures if he could come up with his own," said Ms Davidson.

"We've got 100 days to go and the SNP's case seems seriously to be resting on a guesstimate from a professor responding to a press inquiry."

Document 'destroyed'

Scottish Liberal Democrat leader Willie Rennie said of the first minister: "We know he's an expert on everyone else's figures so he now has the chance to put them right.

"It's simple - he can publish the document that was produced two years ago and sets out the costs for the transition to an independent Scotland."

Mr Salmond responded: "If the chosen expert of the United Kingdom government comes up with an estimate and I describe it as reasonable, isn't it the way to go forward as opposed to misrepresenting his work, overstating by 12 times, and attempting to traduce the reputation of the London School of Economics?"

He told Mr Rennie: "The difference between the document that his lot published yesterday and the document published by the Scottish government is that his lot's document has been destroyed by the very experts who were cited to support it."